writes "The US Food and Drug Administration (FDA) has released (http://www.fda.gov/NewsEvents/Newsroom/PressAnnouncements/ucm291232.htm) its long-anticipated draft guidance for drug makers interested in making generic forms of biological drugs such as enzymes and antibodies. The move could open the door for cheaper versions of some of medicine's most expensive drugs, but it is still unclear how many companies will be willing to tackle the challenges and uncertainties of making 'biosimilar' drugs (http://www.nature.com/news/2010/101103/full/468018a.html) .
Copying biological molecules is a stickier proposition than making ordinary generic medicines because proteins are typically much larger and more complex than small molecule drugs. They are also often produced in cell cultures, and even small variations in how the cells are grown can change the properties of the protein produced (http://www.nature.com/nature/journal/v449/n7160/full/449274a.html)."Link to Original Source